1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus for a motorcycle and a motorcycle equipped with such an exhaust gas purifying apparatus. More particularly, the present invention relates to an exhaust gas purifying apparatus having an improved layout of one or more catalysts.
2. Description of the Related Art
It is well known that nowadays motorcycles with combustion engines have to be equipped with catalysts so as to comply with anti-pollution rules and/or requirements. The catalysts are located inside the main exhaust gas pipe and function to collect and trap the pollutants contained in exhaust gases, thus allowing only permitted substances to be emitted and dispersed into the atmosphere. Accordingly, many efforts have been dedicated over the past few years to the development of exhaust gas pipes and/or apparatuses offering improved anti-pollution performance. However, the development of exhaust gas pipes, in particular for motorcycles, offering adequate performance and efficiency in terms of quantity of pollutants captured and trapped, but still complying with other requirements relating to motorcycles, in particular to motorbikes, such as, for instance, the overall layout, look and appearance, aerodynamics or the like, has revealed to be quite a difficult and challenging task. One of the requirements to be accomplished by an exhaust gas purifying apparatus relates to the activation temperature of the catalysts, namely, the temperature range within which adequate performances in terms of pollutants captured and/or trapped is possible.
In turn, the activation temperature depends on the location of the one or more catalysts. This in particular is due to the fact that the temperature of the catalysts may be influenced by the heat generated by the main engine and dissipated to the outside. Accordingly, placing the catalysts too close to the main engine, in particular too close to the combustion chamber, may result in the catalysts becoming overheated and reaching a temperature higher than the proper activation temperature. Also, this overheating may result in the catalysts not working properly.
A further requirement to be taken into account relates to the fact that the position and disposition of the catalysts influence the overall appearance and dimension as well as the aerodynamic characteristics of the motorcycle. Common catalysts have a length usually between about 10 cm and about 35 cm. Thus, in cases in which at least two catalysts are used, at least two rectilinear portions of the main exhaust gas pipe having the same length or more, each adapted to receive one of the two catalysts, must be provided. Accordingly, even in those cases in which a unique catalyst is needed or used, finding a convenient location for a corresponding rectilinear portion of the main exhaust gas pipe to receive each catalyst (e.g., a catalyst receiving portion of the main pipe) presents a difficult but important challenge.
Moreover, even during assembly of the motorcycle, in particular, during assembly of the exhaust gas purifying apparatus, several problems may occur. In particular, the catalyst receiving portion has to be provided in one piece, and thus, it may become difficult to handle and assemble the catalyst receiving portion. In particular, it may become difficult to assemble the rectilinear portion and/or to introduce the rectilinear portion into spaces having reduced dimensions such as, for instance, into spaces between the engine and the tubes of the main frame as well as into small spaces defined by other components of the motorcycle. Usually, to facilitate the assembly operations, the main exhaust gas pipe includes several detachable portions connected to each other by corresponding joint members, and several portions provided with corresponding several joint members, which determine an appropriate shape for the main pipe. However, assembly is limited by the need to provide a catalyst receiving portion having a predefined length. As a result, if an adequate location is found for the catalyst receiving portion, detachable portions of the main pipe and corresponding joint members can be used along the rest of the main pipe, for instance, in those locations in which detachable portions of reduced length may help in determining an appropriate shape for the main pipe. Furthermore, in the case of special motorcycles, such as, for instance, off-road motorcycles, a predefined minimal distance or gap must be provided between the main exhaust gas pipe and the ground, otherwise the motorcycle cannot adequately be used for the purposes for which it is designed.
In an attempt to meet as many as possible of the criteria and/or requirements described above, several solutions relating in particular to exhaust gas pipes have been proposed in recent years by the manufacturers of motorcycles. For instance, solutions have been suggested in which the one or two catalysts are placed in an area in front of the engine. However, even if, on the one hand, it is possible with such a design to raise the activation temperature of the one or more catalysts within a short time after starting the engine, on the other hand, the problem arises that the resistance of the exhaust gas flow is increased, thus resulting in the output characteristics of the engine being negatively affected.
According to another known solution, the main exhaust gas pipe is allowed to pass along a side of the cylinder block or head, and to extend toward the rear of the motorcycle, with the one or two catalysts being positioned on the side of the cylinder block or head. However, even if it can be appreciated that according to this solution, the two catalysts are not placed too far away from the combustion chamber so that, on the one hand, the time for reaching the activation temperatures is not unduly increased, and on the other hand, other disadvantages arise, relating in particular to the design of the motorcycle. Moreover, the overall dimension of the motorcycle, in particular, in the width direction, is unduly decreased. Further improvements of this solution have been proposed, according to which the catalysts are placed very close to the combustion chamber so as to provide adequate clearance between the catalysts and the legs of the driver and/or passenger. However, as stated above, when this solution is adopted, the temperature of the catalyst may rise excessively, in particular beyond the allowed activation temperature.
A further solution relating to an exhaust gas apparatus for motorcycles is disclosed in, for example, Japanese Patent Application Laid Open Publication No. 2008-94161. According to this solution, an exhaust gas purifying apparatus includes an exhaust gas main pipe extending from the engine of a motorcycle and including a catalyst receiving portion rising upward and substantially vertically. In addition, the receiving portion is located outside, in the motorcycle width the direction, of a rear arm supporting the rear wheel of the motorcycle. However, even if this solution simplifies the assembly operation, it results in an undesirable increase in the transverse dimension of the motorcycle.
Therefore, it is clear from the above description that in spite of all the efforts made to date, the known solutions proposed in the past do not meet the essential requirements which have to be taken into consideration during the design of a motorcycle and an exhaust gas apparatus for a motorcycle. In particular, the proposed solutions do not meet the needs of an exhaust gas pipe offering good performance in terms of functionality and reliability of the catalysts, as well as the needs in terms of the overall look, aerodynamics and reduced dimensions of motorcycles.